Method of making galvanized sheet steel coated on one side



A ril 13, 1965 A. H. WARD 3,173,305

METHOD OF MAKING GALVANIZED SHEET STEEL COATED on ONE SIDE Filed May 4, 1962 Pius-Z 3 29m J1 4i lNVENTOR ALFRED H. WARD Br fi w fw A fforney United States Patent 3,178,305 RETHOD OF MAKING GALVANIZED SHEET STEEL COATED ON ONE SIDE Alfred H. Ward, Brentwood, Pa., assignor to United States Steel Corporation, a corporation of New Jersey Filed May 4, 1962, Ser. No. 192,437 1 Claim. (Cl. 1178) This invention relates to the manufacture of galvanized sheet steel and, in particular, to the manufacture of such material having a zinc coating on one side only, the other side being left bare.

A demand has arisen for galvanized steel sheets coated on one side only. Green et al. Patent 2,894,850 discloses one method of making such product. It is the object of my invention to provide a simpler and more efiicient method.

In a preferred practice, I coat steel strip on both sides with zinc by the hot-dip process. I then progressively dissolve the zinc coating from one side thereby leaving it bare and clean. The removal of the zinc from the one side may be effected by straight chemical action as by bringing it into contact with dilute acid, or by electrolytic action.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating the present preferred embodiment. In the drawings:

FIGURE 1 is a diagrammatic longitudinal vertical section through a line of equipment adapted to carry out my improved method;

FIGURE 2 is a transverse section taken along the plane of line IIII of FIGURE 1 showing a detail; and

FIGURE 3 is a view similar to FIGURE 1 illustrating the apparatus used for a modified practice of my method.

Referring now in detail to the drawings and, in particular, to FIGURES 1 and 2, low-carbon steel strip S leaves a water tank 10, passes between a pair of squeegee rolls 11, then travels over a guide roll 12 andthrough a drier 13 comprising a set of steam coils. Tank may be a quench tank in a hot-dip galvanizing line. Next the strip passes over a series of acid-contacting rolls 14 journaled in a tank 15. The rolls are rubber-covered and the tank is lined with lead or rubber. Partitions 16 of decreasing heights from right to left form separate compartments for the rolls 14, respectively. A dilute aqueous solution of sulphuric or hydrochloric acid, say about 10 or is supplied to the exit end of tank 15 through an inlet 17 and flows over partitions 16 successively then leaves the tank over a weir 18 at the entrance end.

Rolls 14 may be driven at a peripheral speed equal to that at which the strip travels over tank 15. The strip is held in contact with the rolls 14 by hold-down means such as rollers 19 carried by pistons reciprocable in cylinders 20 suitably mounted between adjacent rolls 14. The strip is thus subjected repeatedly to contact with the rolls 14, the surfaces of which carry a film of dilute acid picked up from the compartments in tank 15. The several wiping contacts with acid films progressively dissolve the zinc coating from the underside of the strip, leaving it bare and clean.

, the cathodes.

The acid solution brought into contact with the underside of the strip may tend to creep around the side edges thereof and enter on top of the strip by capillary action. To prevent this, I mount air nozzles 21 above the strip and adjacent the edges thereof, as shown in FIGURE 2. Air under pressure supplied to the nozzles provides jets issuing therefrom which effectively confine the acid solution to the underside of the strip.

On leaving tank 15, the strip passes over a guide roll 22 and through a water scrubber 23, squeegee rolls 24 and a dryer 25. The product is then finished except for shearing to sheets of the desired length. Traction rolls not shown pull the strip through the line and introduce it into a conventional shear.

The removal of zinc from one side of galvanized strip may be eifected electrolytically by the procedure illus trated in FIGURE 3, in which certain parts are the same as in FIGURE 1 and are designated by the same numerals. The strip S, coated with zinc on both side is passed through a tank 26, over guide rolls 27 and 27' and under sinker rolls 23 and 28'. The tank contains a dilute aqueous solution of zinc sulfate with a small amount of sulfuric acid or sulfate radical. A typical composition of the water solution forelectrolytically stripping zinc is:

' Oz. per gal. ZnSO -7H O About 7 Na SO About 10 (to make pH from 3 to 4) Cathodes 29 of zinc are mounted in the tank below the level of the electrolyte and preferably above the path of strip S. Connections are made from a source of direct current, with the polarities indicated, to rolls 28 and 28' surface is quickly removed and deposited on cathodes 29. A very small amount of zinc may be removed from the undersurface of the strip but this will be slight because of the close adjacency of the upper side of the strip to On emerging from tank 26 the strip is finished by the steps already described. Zinc deposited on the cathodes 29 may be reused by adding it to the spelter bath in which the strip is first coated on both sides.

The invention has particular utility in connection with methods for coating sheet steel with a light coating on one side and a heavier or normal-weight coating on the other. When treating such differentially coated material by my invention, of course, the practice Will be to remove the lighter coating and thus expose the underlying base metal without affecting the heavy coating on the other side.

It will be evident from the foregoing that my invention provides a simple, inexpensive and efficient procedure for making galvanized sheets coated on one side only. The apparatus involved, whethe the straight, acid-dissolution or the electrolytic method is employed, can be easily incorporated in conventional strip-galvanizing lines at low cost and operated without introducing any complication Although I have disclosed herein the preferred. em

Patented Apr. 13, 1965 I bodiment and practice of my invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

1 claim:

A method of making sheet steel having a zinc coating on only one side thereof comprising coating a base of sheet steel with zinc on both sides, then wiping one side of the base repeatedly on a rotatable horizontal cylinder the lower portion of the circumference of which dips in a dilute acid solution capable of dissolving zinc, while blowing fluid jets transversely outwardly from points inwardly of the edges of the base onto the side thereof opposite thatin contact with the cylinder.

References Cited by the Examiner UNITED STATES PATENTS Demel 20428 Dunn 204l46 Grupe 20428 Passal 204-146 Gray 204-208 Schaefer et al 204'146 Wasserman 204-446 Zoldas 204-208 Lloyd et al 204206 JOHN H. MACK, Primary Examiner. 

